The present invention relates to a method for selectively extracting a target polynucleotide having a specific base sequence from a polynucleotide mixture sample having a plurality of different sequences or from cells, and an apparatus therefor.
A DNA chip is one of means for detecting a specific base sequence of DNA quickly and easily. It utilizes micropatterning techniques used in microprocessing of semiconductors and the complementarity of DNA. In this technique, DNA sequence of a sample solution is analyzed in the following manner: Single stranded-oligonucleotides as probes having different sequences each of a length of approximately 8-9 bp are immobilized separately onto each of two-dimensionally split individual areas on a substrate; the sample solution containing DNA is added dropwise to the substrate to hybridize the DNA separately with each of probes in each of the areas of the substrate while attaching a fluorescent dye to the hybrids simultaneously in the hybridization step; and the magnitude of the hybridization between the probes and DNA in the sample solution is optically determined through emitted fluorescence to analyze the DNA sequence in the sample solution.
U.S. Pat. No. 4,446,237 discloses a method for capturing a target oligonucleotide (DNA or RNA) as a probe on a solid phase. According to this method, the oligonucleotide in a sample solution is denatured into single strands by heating, which is then immobilized on the surface of a nitrocellulose membrane. S. R. Rasmussen et al. describe another method for capturing a target oligonucleotide sample on a solid phase in Analytical Biochemistry 198, 128-142(1991). According to the method, the phosphate group at the 5xe2x80x2-end is activated by using 1-methylimidazole and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide. The activated polynucleotide is then immobilized onto a polystyrene microplate having a secondary amine on its surface. The activated 5xe2x80x2-end phosphate group reacts with the secondary amine, so that the 5xe2x80x2-end of the polynucleotide is covalently immobilized onto the microplate surface.
As thus described, a target polynucleotide in a sample solution can be captured and analyzed by selectively hybridizing a target polynucleotide (DNA or RNA) with a complementary oligonucleotide immobilized as a probe on a membrane surface. The DNA chip is on the basis of this concept.
Okano et al. describe a method for extracting target polynucleotides by hybridizing the target polynucleotides to probes immobilized on a chip, heating the chip to denature the captured polynucleotides on the probes to separate and collect them from the chip in U.S. Pat. No. 5,607,646.
A method for selectively extracting a target polynucleotide by utilizing difference in rates in electrophoresis of polynucleotides in gel has been in wide use.
The gene analysis technology using a DNA chip described in the above is a technique for hybridizing and analyzing a target polynucleotide (DNA or RNA) by complementarily hybridizing single-stranded polynucleotides derived from the target polynucleotide in a sample solution with a probe (a specific single stranded-oligonucleotide) with a length of 8-9 bp formed on a substrate. This technique is never directed to further extract the captured or hybridized DNA or RNA single stranded-polynucleotide on the probe from the substrate selectively.
Conventional techniques give no consideration of extracting a target polynucleotide to be extracted directly from cells.
According to conventional separating techniques using electrophoresis, the mobility of each of polynucleotides is relative to each other and fluctuates with changes of electrophoresis conditions, and thus identification of an extracted sample solution component is required. In addition, exact separation and purification of a trace quantity of a target polynucleotide is difficult because diffusion in the electrophoresis step can invite contamination of polynucleotides with each other.
It is, therefore, an object of the present invention to provide a process and apparatus for selectively extracting a trace quantity of a target polynucleotide (DNA or RNA) having a specific base sequence rapidly with a high precision.
The invention proposes, to achieve the above object, selective extraction of a target polynucleotide alone from a sample solution by modifying each of independent split areas on the surface of a substrate separately with each of probes (specific oligonucleotides) having different base sequences respectively, hybridizing polynucleotides (DNA or RNA) in the sample solution separately to the probes, and then heating a specific area alone of the substrate selectively to allow a polynucleotide alone complementarily hybridized with the heated probe to liberate from the probe.